Study of Cardiopulmonary Exercise Testing in Women Who Have HER2-Positive Breast Cancer With Mild Cardiotoxicity

Inclusion Criteria:

* Age ≥ 18 years
* Female
* Diagnosed with a HER2-positive solid tumor (stage I-IV)
* Left ventricular dysfunction prior to the start of HER2-targeted therapy, defined by a LVEF \< 53% (or lower limit of normal), or diagnosed with mild cardiotoxicity associated with HER2-targeted therapy, defined by an absolute decrease in LVEF ≥ 10% from pre-treatment to \< 53%
* Planning to undergo treatment with HER2-targeted therapy (e.g. trastuzumab, pertuzumab, or ado-trastuzumab) for a minimum of 3 months (i.e. 4 cycles administered every 3 weeks).
* Willing and able to comply with the requirements of the protocol

Exclusion Criteria:

* Symptomatic heart failure (New York Heart Association Class III or IV)
* Subjects must not have any of the following absolute contraindications to cardiopulmonary exercise testing:

  * Acute myocardial infarction (within 30 days of any planned study procedures),
  * Unstable angina
  * Uncontrolled arrhythmias causing symptoms or hemodynamic compromise,
  * Symptomatic severe aortic stenosis
  * Recurrent syncope
  * Active endocarditis
  * Acute myocarditis or pericarditis
  * Acute pulmonary embolus or pulmonary infarction (within 3 months of any planned study procedures)
  * Thrombosis of lower extremities (within 3 months of any planned study procedures)
  * Suspected dissecting aneurysm
  * Uncontrolled asthma
  * Pulmonary edema
  * Room air desaturation at rest ≤ 85%
  * Respiratory failure
  * Acute noncardiopulmonary disorder that may affect exercise performance or be aggravated by exercise (i.e., infection, renal failure, thyrotoxicosis)
  * Mental impairment leading to inability to cooperate.
* Enrollment onto any other interventional investigational study
* Inability to provide informed consent